This invention is generally directed to processes for the preparation of chalcogenide alloys, and more specifically the present invention is directed to the preparation of chalcogenide alloys in high purity by simultaneously coreducing a solution of the oxides of the elements desired. Accordingly, there is provided in accordance with the present invention a simple, high yield economically attractive, low temperature process for the direct preparation of chalcogenide alloys of high purity. The resulting chalcogenide alloys are useful for the preparation of imaging members, particularly xerographic photocondutive compositions, for electrostatic imaging systems.
The incorporation of selenium or selenium alloys into xerographic imaging members is well known. These members can be subjected to a uniform electrostatic charge for the purpose of sensitizing the surface of the photoconductive layer, followed by exposure of an image to activating electromagnetic radiation such as light, which selectively dissipates the charge in the illuminated areas of the photoconductive insulating member, wherein a latent electrostatic image is formed in the non-illuminated areas. The resulting image may then be developed and rendered visible by depositing thereon toner particles containing resin particles and pigment particles.
Recently, there has been developed layered organic and inorganic photoresponsive devices containing amorphous selenium, trigonal selenium, amorphous selenium alloys, or halogen doped selenium alloys. One such photoresponsive member is comprised of a substrate, a photogenerating layer containing metal phthalocyanine, metal-free phthalocyanine, vanadyl phthalocyanine, or selenium tellurium alloys, and a transport layer containing a diamine dispersed in a resinous binder, reference U.S. Pat. No. 4,265,990.
Commercially available selenium or selenium alloys for use in electrostatic imaging systems, including layered organic and inorganic photoresponsive devices are generally substantially pure, that is, for example a purity of 99.999 percent or greater is desired, since the presence of impurities has a tendency to adversely effect the imaging properties of selenium, and its alloys including the electrical properties thereof, causing copy quality obtained from such devices to be relatively poor in comparison to devices wherein high purity selenium, and selenium alloys are used.
Many processes are known for the preparation of chalcogenide alloys, particularly selenium containing alloys including, for example, melt blending of the elemental substances such as selenium and arsenic in the proportions desired in the final alloy product. Thus, for example, there is disclosed in U.S. Pat. No. 3,634,134 the preparation of arsenic-selenium alloys by mely blending. This method not only involves high temperatures, but in most instances, crystalline materials are not obtained. Further, in many instances depending on the process parameters, the desired alloy is not obtained rather, by following for example the melt blending process, there is obtained an unhomogenous mixture of arsenic, selenium, and an arsenic selenium alloy. Additionally, in these processes, there must be selected for evaporation, high purity arsenic and high purity selenium, that is 99.999 percent pure and processes for obtaining high purity arsenic and selenium precursors require high temperature distillations which are not desirable. A similar melt-blending method for preparing selenium alloys is disclosed in U.S. Pat. No. 3,911,091.
Also there is disclosed in U.S. Pat. No. 4,007,255 a process for preparing stable red amorphous selenium containing thallium by precipitating selenious acid containing from about 10 parts per million to about 10,000 parts per million of thallium dioxide, with hydrazine from a solution thereof and methanol or ethanol containing not more than about 50 percent by weight of water at a temperature between about 0.20 degrees Centigrade and the freezing point of the solution wherein the resulting precipitate is maintained at a temperature of from about a 0.13 degrees Centigrade to about a 0.3 degrees Centigrade.
Disclosed in U.S. Pat. No. 3,723,105 is a process for preparing a selenium-tellurium alloy by heating a mixture of selenium and tellurium containing 1 to 25 percent by weight of tellurium to a temperature not lower than 350 degrees Centigrade to melt the mixture, followed by cooling gradually the molten selenium and tellurium to around the melting point of the selenium tellurium alloy at a rate not higher than 100 degrees Centigrade per hour, and subsequently quenching to room temperature within 10 minutes.
Further, there is disclosed in U.S. Pat. No. 4,121,981 the preparation of a selenium alloy by, for example, electrochemically co-depositing selenium and tellurium onto a substrate from a solution of their ions wherein the relative amount of alloy deposited on the cathode is controlled by the concentrations of the selenium and the tellurium in the electrolyte, and by other electrochemical conditions. Once the selenium tellurium layer deposited on the cathode has reached the desired thickness, deposition is discontinued and the cathode is removed.
Additionally, there is disclosed in U.S. Pat. No. 3,524,745, the preparation of an arsenic antimony selenium alloy by heating a mixture of these materials at a temperature of 600 degrees Centigrade for a period of several hours in a vacuum, followed by air cooling to room temperature. According to the teachings of this patent, the cooled alloy, depending on the initial composition is completely polycrystalline, a mixtue of crystalline and amorphous phases, or completely amorphous.
Furthermore there is disclosed in a copending application U.S. Ser. No. 405,651/82, the disclosure of which is totally incorporated herein by reference, a process for the preparation of chalocogenide alloys of high purity by the simultaneous coreduction of the corresponding esters subsequent to isolation and purification. More specifically there is disclosed in the copending application a process for the preparation of chalocogenide alloys in high purity comprising providing pure esters of the desired chalocogens, and subsequently subjecting the mixture of pure esters to a coreduction reaction with for example hydrazine. In the process of the present invention isolated pure esters are not involved, rather a solution of the oxides are subjected to a coreduction reaction.
While these processes as well as others are suitable for their intended purposes, in most instances, with the primary exception of the process disclosed in the copending application, they require high temperatures and distillation steps. Further, in some instances, these processes result in selenium alloys which have differing electrical properties, which is believed to be a result of inhomogenities known to exist in non-equilibrium glasses. Further, the prior art processes for preparing alloys, with the exception of the process disclosed in the copending application, do not involve the formation of the esters of the desired elements.
There thus continues to be a need for new improved processes for preparing chalcogenide alloys. Additionally, there continues to be a need for an improved simple economically attractive, direct process for the preparation of chalcogenide alloys of high purity. Also, there is a need for improved processes wherein chalcogenide binary and ternary alloys can be obtained in high purity by utilizing substantially similar process parameters and apparatus. Further there continues to be a need for improved processes for the preparation of high purity chalcogenide alloys wherein some of the reactants selected can be recycled. Additionally, there continues to be a need for improved processes for preparing chalcogenide alloys that are homogeneous, are of a crystalline form, and can be obtained in various proportions without using high temperature reaction conditions, and without isolating and purifying any resulting esters. These needs can be satisfied in accordance with the process of the present invention wherein substantially homogeneous chalcogenide crystalline alloys are obtained, by the solution coreduction of a mixture of chalcogenide oxides. In those situations where the rates of reductions of the oxides are comparable, a composition of the resulting alloy mirrors or is substantially identical to the molar composition of the mixture of oxides. In other situations, when the reduction rates are not comparable, the composition of the alloys, may not mirror the molar composition of the elements contained in the mixture of oxides.